
On another book excerpt I found, it is said:
"it provides 5,24 and 28 VDC electrical power and 115 and 26.5 VAC for the operation of all airframe, power plant, [...]"

[EDIT]: and we have 3 instruments, an ampmeter and 2 voltmeters (for each bus) with 2 needles each (for each voltage). At start time, you activate the 2 buses battery power switches, then the 2 inverters ; after a while, amp/volt meters shows respective value and you are able to start the 2 engines.